Diabetes mellitus is a metabolic disorder where the body does not use energy properly. One of the symptoms of diabetes is sudden and unexplained weight loss. Excessive hunger and thirst are two other symptoms, and patients with untreated diabetes may find themselves losing weight even as they are eating and drinking more than usual. There are several reasons why people with diabetes lose weight, but to better understand why weight loss occurs, you need to explore how diabetes affects the body.

Digestion and Energy Production
Under normal circumstances, your body converts food into sugar during the digestive process. The sugar enters your bloodstream and the pancreas, a small organ behind the liver, release a chemical known as insulin. Insulin tells all the cells in the body to take sugar from the blood and convert it to energy, which the cells use as fuel.
Types of Diabetes
There are two types of diabetes mellitus – type 1 and type 2. With type 1 diabetes, the body either does not make insulin, or it does not make enough, and the cells never get the chemical signal to absorb sugar from the blood. With type 2 diabetes, the body makes insulin but the cells do not respond to the chemical signals, or they respond incorrectly. In both instances, the sugar stays in the bloodstream, where the body is unable to use it for energy.

Effects of Diabetes
When the cells are unable to use sugar for energy, they send a signal to the brain that they need more fuel. The brain then triggers the hunger response to encourage you to eat, hence the excessive hunger that often occurs with diabetes. However, the more you eat, the more sugar ends up in your bloodstream instead of in the cells, where it belongs. You kidneys then have to work overtime to clear the sugar from your blood through the urine. Your kidneys have to use a lot of water to flush out the sugar, hence the excessive thirst.

Diabetes and Weight Loss
In addition to triggering the hunger response, the brain also breaks down muscle tissue and fat in an effort to provide energy for the cells. It is this process that causes the sudden weight loss associated with diabetes. If the condition continues, untreated, the body can go into ketoacidosis, according to “The Principles of Anatomy and Physiology.” In ketoacidosis, the body produces chemicals called ketones from breaking down fats too quickly. These ketones enter the bloodstream and make the blood acidic, which can cause organ damage and even death.